what size cable do i need

[lukesparky123]

hi there can any body help me work this calculation out please its for a garage/office above.
the lighting works out to 2400 watts and they want 6 3kw heaters at 18000 watts and then 13 double sockets and two electric garage doors. so just to re cap--- lights 2400 watts, heaters 18000 watts , two garage doors and 13 double sockets.

so what cable size do you reckon guys ?​

 

[bugsy]

which element of the installation are you refering to

 

[i=p/u]

theres a bit more to take into consideration, like installation methods, distances and knowing ehats going to be plugged into them sockets . but here goes your lights =11A so 1.5mm your heaters pull 13A each so you might get away with 2 heaters on 2.5mm but depends how cables is installed. the sockets could go on a ring circuit 2.5mm but depends on the load and your garage doors depends on power they use

 

[i=p/u]

still loads to fiddle with like diversity/separation of circuits for practical reasons

 

[lukesparky123]

sorry the swa needed to feed the garage about 25 mtrs is what i need.

 

[i=p/u]

il say 25mm to cover your butt

 

[lukesparky123]

well i worked it out around 90amps 16mm swa. The job was suppose to be done by another electrician who has put 10mm swa in so i said it was too small so abit of a dispute going on at the moment so i thought i would ask around a bit.

 

[i=p/u]

can you use diversity on the circuits, then use diversity on overall or just the once.i dont know this

 

[yellowvanman]

Ask the question will all the lights be on with all the heaters and then some more load on the ring main at the same time? If so then size accordingly, if not try looking at using some diversity.

Garage doors shouldn't need to be considered too much as they work occassionally and for a short time each time!

 

[bugsy]

theres a bit more to take into consideration, like installation methods, distances and knowing ehats going to be plugged into them sockets . but here goes your lights =11A so 1.5mm your heaters pull 13A each so you might get away with 2 heaters on 2.5mm but depends how cables is installed. the sockets could go on a ring circuit 2.5mm but depends on the load and your garage doors depends on power they use

me thinks you might want to split the lighting, I would suggest heaters on 4mm radials, x3, garage doors radial - seperate RCBO sockets on rings feed 16mm SWA ( depends on Run )

 

[nickblake]

Fisrst thing i would do is check the main incomming supply , you say 25 meters of swa so whats this for ??? to supply the garage , thats alot of heating to have you considered using the Farho Farho electric radiators : Home or roinet http://www.roinet.com/ these guys do a low energy heater that costs 60% less to run and is more economical to run they will also visit your site and advise you at no cost , where you say cable size is this for the swa you have mentioned or the complete install if its the SWA then you will need 25mm 3 core ,diversity wise there is no diversity for the heaters and your loading will be 78 amps if all in use at the same time and belive you me they will be at times 11 amps for lighting plus 26 amps for your socket , so to work it out with diversity lighting is 90% of total demand as its commercial ,heating no diversity allowed , and the sockets 100% of of current demand and 40% of current demand for every other point

 

[nickblake]

heaters pull 13A each so you might get away with 2 heaters on 2.5mm but depends how cables is installed.


I=P/U >>> Any appliance 3kw or greater should be on its own circuit , 26 amps on a 2.5 mm cable what size breaker would you protect that with then ???

 

[andekoch]

without knowing more I would guess diversity at about 70A (all lights, 3 heaters and 24A rest) so depending on volt drop 10mm seems on the small side. Get him to show how he did his diversity calc. As long as he can justify it and his justification makes sense then ok. Seems small to me but see how he worked it out.

 

[i=p/u]

nickblake you shot me down to earth again, forget my post above

 

[bugsy]

lighting 10a, heating 10a + 32.5a ( based on non commercial which I think this is ) sockets dont know use so 20a doors 0 calc load 62.5a
So you might get away with 10mm dependent on run and installation method